The ruby (guess it's one) looks very awesome and realistic, but some parts of the picture appear to be way less detailed e.g. the coins which look a lot as if beeing made from wood due to their gloomy "skin".But anyhow: This is very great work (and I'm not the one to open my mouth for criticising such masterpieces )

I like how the gem goes and into the darkness so you only see its reflection. The strong lighting is good, I can tell where it comes from - a thing I tend to forget to do when I draw, bah.

Although, if those coins and maybe platform is metallic, I think it'd be shinier and with a sort of stiff lighting on it. At least the coins. Though overall, you have various textures from the gem to sand and so forth that really makes it pop too. : )